"use strict" // JS中‘和“好像没有区别
let name, admin;
name = 'John';
admin = name;
alert(admin);
let ourPlanetName = 'Earth';
let currentUserName = 'John';
alert(Infinity);
alert('Not a number' / 2);
alert(NaN - 2);
alert(NaN * 2);
alert(NaN ** 0);